System and method to reduce acoustic signature using profiled stage design

ABSTRACT

To reduce noise and thereby increase turbine efficiency, the end walls and airfoils of a turbine are designed to reduce or eliminate radial pressure gradients on rotor blades and their incipient secondary flow vortices which may noisily excite downstream blade and vane rows. Instead of generating inefficient noise, the fluid energy may be properly directed into the shaft as efficient work.

BACKGROUND

When the radial pressure gradient in the fluid stream of a turbine isminimized or eliminated, turbine stage efficiency can be significantlyimproved. Typical turbine inefficiencies may include noise productionfrom several fluid dynamic sources, including wake cutting, highvelocity fluid, and turbulent flow fields, including secondary flowvortices. The noise generally results from reflecting and turbulent wavefields incident upon the several stationary and moving blades downstreamfrom a blade set that receives irregular pressure differentials andconverts them into secondary flow vortices. As explanation, when apressure gradient incident on a rotating blade set is intense enough,transient or sustained separation of fluid flow may occur in thevicinity of the trailing edges of the blades. This separation of fluidflow can result in secondary flow vortices directed downstream atstationary and moving blades, thus producing high-intensity noiseinstead of directing the fluid energy into the output shaft for powergeneration.

What is needed, therefore, is a system designed to reduce radialpressure gradients incident upon rotating blades and thereby direct thefluid energy into the output shaft instead of into the creation ofnoise.

SUMMARY

Embodiments of the disclosure may provide a turbine having a workingfluid. The turbine may include at least one set of rotor blades mountedradially symmetrically about a rotating shaft, wherein each rotor bladehas a hub and a tip, and at least one stator axially-spaced from the atleast one set of rotor blades and mounted radially symmetrically aboutthe rotating shaft, wherein the at least one stator defines a pluralityof radially-spaced vanes having inner and outer end walls that defineend wall passages, wherein the end wall passages have a profile shapedto direct a working fluid to a plane substantially tangent to the innerand outer end walls.

Embodiments of the disclosure may further provide a stator for aturbine. The stator may include an inlet and an outlet, wherein theoutlet is adjacent to at least one rotor blade having a hub and a tip,and a plurality of inner and outer end walls extending from the inlet tothe outlet and defining a plurality of end wall passages having innerand outer radial limits, wherein the end wall passages have a profileconfigured to direct a working fluid to a plane substantially tangent tothe inner and outer radial limits, wherein the plurality of inner andouter end walls are configured to substantially eliminate the radialpressure gradients incident between the hub and the tip of the at leastone rotor blade, thereby attenuating the resultant acoustic signature.

Embodiments of the disclosure may further provide a method of reducingturbine acoustic signature. The method may include introducing a workingfluid into a turbine having at least one stator adjacent to andaxially-spaced from at least one rotor blade, wherein the statorcomprises a plurality of radially-spaced vanes, each vane having aninlet and an outlet and defining a profile of an end wall passageincluding an inner and outer end wall, receiving the working fluidthrough the inlet of the end wall passage, channeling the working fluidthrough the profile of the end wall passage, and directing the workingfluid out the outlet of the vane and substantially tangent to the innerand outer end walls, thereby substantially decreasing the radialpressure gradient incident between a hub and a tip of the at least onerotor blade, and thereby attenuating the resultant acoustic signature.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying Figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale. In fact, the dimensions of the variousfeatures may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a partial diagrammatic, longitudinal sectional viewof an exemplary turbine according to one or more aspects of the presentdisclosure.

FIG. 2 illustrates a fragmentary view of a pair of turbine stagesaccording to one aspect of the present disclosure.

FIG. 3 illustrates an axial depiction of the defining lines for theprofiles of the end wall sections, according to one aspect of thepresent disclosure.

FIG. 4 illustrates a radial view of the convex and concave surfaces ofan exemplary set of stator vanes.

DETAILED DESCRIPTION

It is to be understood that the following disclosure describes severalexemplary embodiments for implementing different features, structures,or functions of the invention. Exemplary embodiments of components,arrangements, and configurations are described below to simplify thepresent disclosure, however, these exemplary embodiments are providedmerely as examples and are not intended to limit the scope of theinvention. Additionally, the present disclosure may repeat referencenumerals and/or letters in the various exemplary embodiments and acrossthe Figures provided herein. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various exemplary embodiments and/or configurationsdiscussed in the various Figures. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact.Finally, the exemplary embodiments presented below may be combined inany combination of ways, i.e., any element from one exemplary embodimentmay be used in any other exemplary embodiment, without departing fromthe scope of the disclosure.

Additionally, certain terms are used throughout the followingdescription and claims to refer to particular components. As one skilledin the art will appreciate, various entities may refer to the samecomponent by different names, and as such, the naming convention for theelements described herein is not intended to limit the scope of theinvention, unless otherwise specifically defined herein. Further, thenaming convention used herein is not intended to distinguish betweencomponents that differ in name but not function. Further, in thefollowing discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to.” All numericalvalues in this disclosure may be exact or approximate values unlessotherwise specifically stated. Accordingly, various embodiments of thedisclosure may deviate from the numbers, values, and ranges disclosedherein without departing from the intended scope.

According to an exemplary embodiment of the present disclosure, toreduce noise and thereby increase turbine efficiency, the end walls andairfoils of a turbine may be designed to reduce or eliminate radialpressure gradients and their potential secondary flow vortices which mayexcite downstream blade and vane rows into the production of noise. Inparticular, by channeling reflecting and turbulent flow waves into acontinuously-flowing shape through the end walls and airfoils, the fluidflowpath of the working fluid becomes generally linear in the desireddirection of flow. Consequently, with a generally linear flowpath, theworking fluid may be channeled directly into the succeeding rotor rowwith a minimal hub to tip velocity differential. Thus, the fluid energymay be directed into the shaft to create work, rather than into thegeneration of inefficient noise.

FIG. 1 illustrates an exemplary turbine 100 according to at least oneaspect of the present disclosure. In an exemplary embodiment, theturbine 100 may be a multiple-stage steam turbine. The turbine 100 maybe composed of a plurality of stages wherein a first stage 101 mayinclude a set of rotor blades 102, axially-spaced from and interleavedwith a set of stator vanes 104. The first stage 101 may be followed byany number of succeeding stages, The rotor blades 102 may be configuredas a circular moving blade set, while the stator vanes 104 may beconfigured as a circular or semi-circular stationary blade set, eachblade set having blades mounted symmetrically radial about a rotatingshaft 106. In an exemplary embodiment, the first stage 101 may be animpulse turbine stage, but may also be a reaction turbine stage. Thepresent disclosure, however, may be less effective in a reaction machinesince there is no real danger of the hub pressure at the rotor inletdropping below the pressure at the rotor exit.

The rotor blades 102 may each be provided with a root 108 configured tocouple the blades 102 to the rotating shaft 106 which rotates around acentral axis of the turbine 100. The stator vanes 104 may be in a fixedarrangement, typically mounted circumferentially to the outer casing 110of the turbine 100 and extending inwardly therefrom.

In exemplary operation, a fluid, such as steam, air, products ofcombustion, or a process fluid such as CO₂ or other fluid may be used asthe working fluid. In an embodiment using steam, the fluid may includeinjected into the turbine 100 and follow a plurality of channels orpassageways, depicted by the arrows 112, thus channeling itself throughthe various stages of rotor blades 102 and stator vanes 104. As thesteam passes through the various stages of the turbine 100, the statorvanes 104 may be configured to direct the fluid into contact with thesubsequent set of rotor blades 102, thereby causing the shaft 106 torotate and produce work.

However, if the fluid flow directed at the rotor blades 102 is composedof a heightened hub-to-tip pressure gradient, the rotor blades 102 maybecome agitated and create noise, or they may produce secondary flowvortices, potentially exciting downstream blades 102 or vanes 104 whosevibrations will also create noise. According to one aspect of thepresent disclosure, to reduce or eliminate the production of noise, thepassageways 112 of the vanes 104 may be profiled in a manner thatdirects the fluid flow in a generally uniform pressure toward the rotorblades 102.

Referring now to FIG. 2, illustrated is an exemplary embodiment of apair of turbine stages 201 a, 201 b according to at least one aspect ofthe present disclosure. The stages 201 a, 201 b may each consist of aplurality of stator vanes 104 followed by a plurality rotating blades102, wherein the arrow 112 denotes the direction of fluid flow throughthe particular stages 201 a, 201 b. Although not fully illustrated, eachstage 201 a, 201 b may consist of a body of revolution about therotational axis of the turbine 100.

In particular, FIG. 2 illustrates a pair of stator vanes 104 and a pairof rotating blades 102, wherein each rotating blade 102 may include atip 212 and a hub 214. As illustrated, each stator vane 104 may definean end wall passage 202 extending from an inlet 203a to an outlet 203band configured to direct fluid flow into the subsequent set of rotatingblades 102. The end wall passage 202 may include an outer section 204and an inner section 206, wherein each section 204, 206 may incorporatea given profile 208, 210, respectively.

When fluid flows in the end wall passage 202 the flow is considered“attached” if it flows continuously in one direction in the spacedefined between the outer section 204 and the inner section 206.Although the velocity profile of the flow will generally proceed in anequivalent direction, it may change depending on whether the flow islaminar or turbulent. In typical operations, there will be a smallboundary layer of slower flow adjacent to each profile 208, 210, but theflow in this boundary layer will be in the same direction as the flow inthe rest of the space. If the boundary layer gets too thick that theflow within it reverses, a phenomenon called “hub separation” may occur,potentially creating eddy currents.

In turbines, the flow being accelerated through the end wall passage 202generally flows in a direction tangent to the circumference at the pointin the end wall passage 202 where it turns from the axial direction andis thereby accelerated. The flow continues “straight” in space, but theboundary profiles 208, 210 both curve inward or downward, tending tobunch up the flow at the outer profile 208 (locally curving toward it)and flow away from the inner profile 210 (locally curving away from it).As can be appreciated, this results in an uneven velocity flowdistribution, and is the type of behavior that the present disclosure isdesigned to prevent or remedy.

During turbine 100 operation, a pressure gradient incident across thetip 212 and hub 214 of a rotor blade 102 may also generate “hubseparation.” For example, the centrifugal acceleration of the workingfluid in a turbine 100 generally forces, or “stirs,” the fluid away fromthe hub 214 and creates a substantially higher pressure near the tip 212of the rotating blade 102 than at the hub 214. However, suppressing thepressure at the hub 214 may potentially cause a negative reaction,typically in the form of a significant potential pressure rise acrossthe hub 214 sections of the blade 102. Blade 102 reaction may becharacterized by the pressure drop across the blade 102 row divided bythe pressure drop across the end wall passage 202. Since this pressurerise at the hub 214 cannot generally be supported, the hub 214 sectionsof the blade 102 may “separate,” resulting in a radial pressure gradientflowing out of the end wall passage 202.

The result of this pressure gradient on the rotating blade 102 is thatsecondary flow vortices may potentially develop and excite or vibratedownstream objects, such as rotor blade 102 and stator vane 104 rows.The excitation or vibration of rotor blade 102 and/or stator vane 104rows may produce high-intensity noise representing fluid energy that isinefficiently wasted as noise production instead of being directed intothe output shaft 106 for generation of power.

According to one exemplary embodiment of the present disclosure, theprofiles 208, 210 may be configured to provide a constant and equalizedpressure gradient across the rotating blades 102, thereby reducing oreliminating secondary flow vortices. Particularly, the specific profiles208, 210 of the end wall passages 202 may be configured to mimic thetangential fluid flow exiting the stator vane 104 and make the exitingpressure substantially uniform as it extends from the hub 214 to the tip212 of the subsequently located rotating blade 102. Uniform pressuresincident on the rotating blades 102 minimize and/or prevent hub 214“separation” that would normally result in the production of downstreamnoise, as described above.

The curvature, or shape, of the end wall 202 profiles 208, 210 may bederived via axial and radial projections, upstream from the rotatingblades 102, from a pair of lines of revolution about a centerline of theturbine 100. Referring to FIG. 3 (in combination with FIG. 2),illustrated is a depiction of the lines of revolution 302, 304 for theouter section 204 and the inner section 206, respectively, of the endwall 202. As shown, the lines of revolution 302, 304 may be drawn fromthe centerline 306 of the turbine 100. In the axial direction, the outerend wall section 204 may have its profile defined by an extent, tangentto the tip 212 of the rotating blade 102, obtaining between points “a”and “b”. Also, in the axial direction, the inner end wall section 206has its profile defined by an extent, tangent to the hub 214 of therotating blade 102, obtaining between points “c” and “d”.

FIG. 4 shows a radial view of an exemplary stator vane 104 body, wherethe convex and concave surfaces 402, 404, respectively, are illustrated.Inscribed between the surfaces 402,404 is a mean line 406 which radiallyextends between points “e” and “f”. In an exemplary embodiment of thedisclosure, the mean line 406 may be the axially-defining component forthe profiles 208, 210 and configured to allow the profiles 208, 210 tomimic tangential fluid flow. In alternative exemplary embodiments, inlieu of the mean between the surfaces 402, 404, the axially-definingcomponent for the profiles 208, 210 can comport to either the convexsurface 402 or the concave surface 404, or any other representative flowline derived through geometric or fluid dynamic calculation.

According to the present disclosure, with a substantially tangentialfluid flow exiting the end wall 202, the incident pressures on therotating blades 102 from the hub 214 to the tip 212 may be substantiallyuniform, and thus reducing or completely eliminating any secondary flowvortices. Particularly, using a profiled end wall 202 may direct aworking fluid onto the rotating blades 102 such that the pressure at thehub 214 is equal to the pressure at the tip 212. By reducing the hub 214to tip 212 pressure gradient incident on the rotating blades 102, asexplained above, a reduction of downstream turbine 100 acousticsignature may result, thereby increasing turbine 100 efficiency.

The foregoing has outlined features of several embodiments so that thoseskilled in the art may better understand the detailed description thatfollows. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions andalterations herein without departing from the spirit and scope of thepresent disclosure.

1. A turbine, comprising: at least one set of rotor blades mountedradially symmetrically about a rotating shaft, wherein each rotor bladehas a hub and a tip; and at least one stator axially-spaced from the atleast one set of rotor blades and mounted radially symmetrically aboutthe rotating shaft, wherein the at least one stator defines a pluralityof radially-spaced vanes having inner and outer end walls that defineend wall passages, wherein the end wall passages have a profile shapedto direct a working fluid to a plane substantially tangent to the innerand outer end walls.
 2. The turbine of claim 1, wherein the profile ofthe end wall passages is configured to substantially eliminate theradial pressure gradient incident between the hub and the tip of eachrotor blade, whereby the resultant acoustic signature of the turbine isattenuated.
 3. The turbine of claim 1, wherein the turbine is amultiple-stage steam turbine.
 4. The turbine of claim 1, wherein each ofthe radially-spaced vanes have a convex surface and a concave surfacewith the convex surface of one vane and the concave surface of anadjacent vane defining the end wall passages.
 5. The turbine of claim 4,wherein the convex and concave surfaces are configured to cause theworking fluid passing through the end wall passages to follow a pathdefined by a mean of the adjacent convex and concave surfaces.
 6. Theturbine of claim 1, wherein the inner and outer end walls are configuredto make the working fluid pressure at the hub substantially equal to theworking fluid pressure at the tip.
 7. The turbine of claim 1, whereinthe vanes are configured to direct fluid passing through the end wallpassages circumferentially about and radially-spaced from a center lineof the turbine.
 8. A stator for a turbine, comprising, an inlet and anoutlet, wherein the outlet is adjacent to at least one rotor bladehaving a hub and a tip; and a plurality of inner and outer end wallsextending from the inlet to the outlet and defining a plurality of endwall passages having inner and outer radial limits, wherein the end wallpassages have a profile configured to direct a working fluid to a planesubstantially tangent to the inner and outer radial limits, wherein theplurality of inner and outer end walls are configured to substantiallyeliminate the radial pressure gradients incident between the hub and thetip of the at least one rotor blade, thereby attenuating resultantacoustic signature.
 9. The stator of claim 8, wherein, taken along anaxial cross-sectional view, the tip of the at least one rotor blade issubstantially tangent to the outer radial limit and the hub of the atleast one rotor is substantially tangent to the inner radial limit. 10.The stator of claim 8, wherein the profile is configured to direct fluidpassing through the end wall passages circumferentially about andradially-spaced from a center line of the turbine.
 11. A method ofreducing turbine acoustic signature, comprising: introducing a workingfluid into a turbine having at least one stator adjacent to andaxially-spaced from at least one rotor blade, wherein the statorcomprises a plurality of radially-spaced vanes, each vane having aninlet and an outlet and defining a profile of an end wall passageincluding an inner and outer end wall; receiving the working fluidthrough the inlet of the end wall passage; channeling the working fluidthrough the profile of the end wall passage; and directing the workingfluid out the outlet of the vane and substantially tangent to the innerand outer end walls, thereby substantially decreasing the radialpressure gradient incident between a hub and a tip of the at least onerotor blade, and thereby attenuating resultant acoustic signature. 12.The method of claim 11, wherein the turbine is a multiple-stage turbineand the working fluid is steam.
 13. The method of claim 11, wherein eachof the radially-spaced vanes have a convex surface and a concave surfacewith the convex surface of one vane and the concave surface of anadjacent vane defining the end wall passages
 14. The method of claim 11,wherein, taken along an axial cross-sectional view, the tip of the atleast one rotor blade is substantially tangent to the outer end wall ofthe end wall passage and the hub of the at least one rotor blade issubstantially tangent to the inner end wall of the end wall passage. 15.The method of claim 11, wherein each of the radially-spaced vanes have aconvex surface and a concave surface with the convex surface of one vaneand the concave surface of an adjacent vane defining the end wallpassages.
 16. The method of claim 15, wherein the convex and concavesurfaces are configured to cause the working fluid passing through theend wall passages to follow a path defined by the mean of the adjacentconvex and concave surfaces.
 17. The method of claim 11, wherein theconvex and concave surfaces are configured to cause the working fluidpassing through the end wall passages to follow a path defined by theconcave surface.
 18. The method of claim 11, wherein the convex andconcave surfaces are configured to cause the working fluid passingthrough the end wall passages to follow a path defined by the convexsurface.
 19. The method of claim 11, wherein the working fluid one ofair, products of combustion, or a process fluid such as carbon dioxide.